I think the connection to car allowance is that many companies make it a rule that if you have a company car you arrive in it each day and it is available at 'the drop of a hat' so you can go on a business trip with no notice. The sooner company cars are taxed out of existence the better.

p.s. my mate got around this by driving in once, leaving his car in the directors car park, got a lift home, then cycled the rest of the week…after a while they were happy for him to remove his car from the prime directors parking spots and cycle in leaving his car at home.